103

A Scientific Approach to Writing for Engineers and Scientists, First Edition. Robert E. Berger.

© 2014 The Institute of Electrical and Electronics Engineers, Inc. Published 2014 by John Wiley & Sons, Inc.

Multiple-Item Lists

10

Technical writing often requires the use of lists that contain more than two items. These

lists can range from the very simple (where each item contains only one word or a few

words) to the very complex (where each item of the list contains multiple sentences). As

we shall see, the principle of equivalence, introduced in Chapter 9, also applies to lists

of three or more items.

10.1 Simple Lists

A simple list is one that requires only commas to separate its items. The items of such

lists can vary from a single word to a long phrase or clause.

Punctuation of Simple Lists to Ensure EquivalenceIn preparing simple lists with multiple items, the main consideration is to ensure that

the equivalence principle is satisfied. In the following examples, the individual items in

the list are underlined, and the basis for equivalence is provided in the parenthetical

remarks:

104 MULTIPLE-ITEM LISTS

1. One example of the use of pH measurement is in chemical processing,

where titration often is used to drive the pH to a certain level, in order to

initiate, maintain, optimize, or terminate reactions.

(Each item of the list is the verb portion of an infinitive.)

[180]

2. Advanced instrumentation for the power grid infrastructure can improve

efficiency by enabling true dynamic rating, identifying grid operational

instability, and improving operator response to contingencies.

(Each item of the list is a gerund phrase, the object of the preposition by.)

[181]

3. New gasifier designs are needed to produce a high-methane-content

syngas that can be utilized by various industries, upgraded to synthetic

natural gas for pipeline transport, or used by utility-scale fuel cells.

(Each item of the list contains (1) a past participle that completes the

compound verb beginning with can be and (2) a prepositional phrase.)

[182]

As seen in the examples above, all items of the list are separated from one another by

commas, including the last item. Although some grammar books or Web sites suggest

that, in a list, the comma before the word and is optional, these same sources often

acknowledge that the final comma is preferred in formal writing. Hence, this usage is

recommended for technical writing. By using the comma before the word and, the

chances of any misunderstanding is minimized. The following example is presented to

demonstrate the potential for misunderstanding when the final comma is omitted:

4. The graphite layer in the bipolar plates of PEM fuel cells contributes to

electrical conductivity, flexibility, resistance to corrosion and gas permeation. [183]

In the preceding example, the author intends to say that gas permeation is one of four

attributes of the graphite layer. However, it is possible that a reader may misinterpret the

list and assume that it is an unbalanced three-item list—that is, the last major item of the

list has two items. Under this interpretation, the graphite layer would provide resistance

to corrosion and resistance to gas permeation, exactly the opposite of what was intended

by the author.

(Of course, one may counter that if the latter interpretation had been intended, the author

would have inserted the word and before the word resistance, consistent with the

guidance provided in Section 9.2 for unbalanced lists. However, readers of technical

material—especially reviewers of proposals—tend to be busy and may overlook such

nuances. Such potential misunderstandings, in which a reader could infer the opposite

of what is intended, are not risks worth taking.)

Position of the List Within the SentenceIn the preceding examples of simple lists, the list appeared at the end of the sentence,

and no further punctuation was required. Likewise, no further punctuation usually is

required when the list occurs (1) at the end of an introductory qualifier (as illustrated in

SIMPLE LISTS 105

Example 1 below) or (2) at the end of the core of the sentence, even when the core is

followed by a trailing qualifier (as illustrated by Example 2 below):

1. When lithium-ion cells are exposed to high temperatures, overcharge,

over discharge, or short circuits, the extreme conditions not only could

cause cell failure but also could lead to fires or even explosions.

(The list occurs at the end of the introductory qualifier.)

[152]

2. The converters must be highly integrated, power effective, and low cost,

in order to satisfy the requirements for next-generation high energy

physics experiments.

(The list occurs at the end of the core, which is followed by a nonrestrictive

infinitive phrase.)

[184]

In Example 2, it is clear from the context that the trailing qualifier pertains to the entire

list and not merely the last item. The latter case—where a qualifier pertains only to an

individual item of the list—can be resolved by using semicolons to separate the major

items in the list. The use of semicolons will be addressed in the next section.

Sometimes, the position of the list within the sentence may require a higher order of

punctuation, in order to avoid any misunderstanding that may arise from the presence of

so many commas. The following example illustrates a list that is fully contained within

the core:

3. The gas turbine market for electrical utility power generation – along with

the market for mid-sized gas turbine generators for industrial plants, hos-

pitals, and other facilities – exceeds five billion dollars per year.

(The qualifier, a major prepositional phrase, containing the list is fully

contained within the core of the sentence; by enclosing the qualifier within

dashes, a potential misunderstanding can be avoided.)

[185]

Four other examples of lists that were fully contained within the core were presented in

Section 7.2. For those examples as well, dashes were used to separate the qualifier con-

taining the list. Two of those examples are repeated below:

4. The fiber-reinforced plastic composite will combine desirable properties –

such as thermal robustness, electrical conductivity, and radiation

shielding – suitable for use in satellite components.

(The nonrestrictive qualifier is a such as phrase containing a list of nouns)

[30]

5. New buffer materials and depostion processes – which simplify the struc-

ture, improve manufacturability, and reduce manufacturing costs  – are

needed to help ensure that this emerging technology reaches the

commercial market.

(The nonrestrictive qualifier is a which clause containing a list of verb phrases.)

[118]

106 MULTIPLE-ITEM LISTS

As pointed out in Section 7.2, parentheses also could be used to separate an internal

qualifier that contains a list.

Finally, keep in mind that a higher order of punctuation also would be preferred if a list

were fully contained within an introductory or trailing qualifier (as opposed to having

the list at the end of such a qualifier); however, such occurrences are rare.

10.2 Use of Semicolons to Distinguish Items in Complex Lists

When lists contain items that themselves contain commas, including items that them-

selves contain an embedded list with more than two items, a higher order of punctuation

should be used. For such purposes, the semicolon is the punctuation mark of choice. The

semicolon also is preferred when each item is a complete sentence. The first set of

examples below illustrates the use of semicolons for lists within lists:

1. Applications that require such measurements include air quality control;

atmospheric chemistry; mapping of agricultural, landfill, and traffic emis-

sions; and pipeline leak detection.

(The third major item contains a three-item list.)

[186]

2. This project will develop a defect-free membrane that has high flux, high

selectivity, and high resistance to contaminants; is able to handle high

pressure and temperature; and is durable and economical.

(The first major item contains a three-item list.)

[187]

3. Commercial applications should arise in precision farming (monitoring

crop yields, health, disease management, irrigation); the marine and

coastal environment (phytoplankton detection, coastal mapping, ocean

color, river deltas, iceberg tracking); natural hazard and pollution moni-

toring (oil spills, floods, forest fires, volcanoes); oil, gas, and mineral explo-

ration (for collection of geologic and structural terrain information, and to

assist in planning field work); medical diagnostics such as photodynamic

therapy; and spectroscopic medical image processing.

(The fourth major item contains a three-item list.)

[188]

Note that most of the six major items in Example 3 contain parenthetical remarks, many

of which include lists themselves. Despite this added complexity, the semicolon serves

as an adequate means of separating the major items of the primary list. Note also that the

final item of a list using semicolons is preceded by a semicolon and the word and (anal-

ogous to the use of a comma and the word and that precedes the final item of a simple

list).

In the next set of examples, semicolons again are used as the preferred punctuation

because of the presence of commas within one or more of the items (even though the

item itself does not contain an embedded list):

NUMBERED ITEMS IN A LIST 107

4. The Phase I project involves the identification of the parameters for an

electron model of the accelerator; simulations to find an optimal magnetic

field configuration; and a conceptual design of the RF cavity system,

based upon the superposition of axisymetric and dipole modes.

(The third major item contains a nonrestrictive participle phrase.)

[189]

5. The design will accommodate specific feedstock requirements for

fabricating fuel pellets; adapt to the inconsistency of diverse types of bio-

mass; and create a consistent, reliable pelletized fuel.

(The third major item contains multiple adjectives separated by a comma –

more on adjectives in Section 12.1.)

[190]

6. The thin-film coating technology should find use in hard, wear- resistant

diamond coatings for cutting tools; free-standing films for x-ray windows;

and scratch resistant diamond coatings for various types of optics,

including eyeglasses.

(Elements of Examples 4 and 5 are both present here: the first major item

contains adjectives separated by a comma; the third major item contains a

nonrestrictive including phrase.)

[124]

Finally, semicolons are preferred over commas to separate items that are complete

sentences:

7. In this project, a design specification for the hydrogen home fueling

system will be identified and defined; long-term stability tests will be per-

formed at stack level; and the process economics will be evaluated.

(Each item of the list is a main clause of a triple-compound sentence.)

[191]

Because the semicolon is accepted for separating the main clauses of a compound sen-

tence (see Section 9.3), and because the semicolon also is used to separate items in a list,

it is the ideal punctuation mark for separating a list of otherwise complete sentences.

10.3 Numbered Items in a List

Sometimes, even if semicolons are used, ambiguities can arise when the reader attempts

to distinguish the items in a list. In such cases, the items in the list should be numbered,

in order to remove any chance of misinterpretation. Numbers also should be used if the

items in a list are long, if the items represent a particular sequence of steps, or if the list

is introduced by reference to a particular number of items. In numbering the items in a

list, the following points should be noted:

Numbered lists may be appropriate for both two-item lists and multiple item

lists. Also, the use of numbers may be appropriate whether or not semicolons are

used.

108 MULTIPLE-ITEM LISTS

In general, the use of numbers in lists does not affect the guidelines for punctuation.

However, there is one exception: for two-item numbered lists, it is optional to insert

a comma or semicolon before the word and that precedes the second item—the use

of this option can further distinguish the two items for the reader.

When using numbers in a list, I prefer enclosing the number within left and right

parentheses—for example, (2). While a single right-hand parenthesis is some-

times used—for example, 2)—most readers expect to see parentheses appear in

pairs.

The use of numbered lists should be limited to one numbered list per paragraph—a

second numbered list in the same paragraph can be visually disconcerting to a

reader. If the use of a second numbered list appears to be essential, I recommend

that you begin a new paragraph.

Numbers Used to Avoid AmbiguityIn some situations, the use of semicolons alone is not sufficient to distinguish the dif-

ferent items in a list. In the first of these situations, some ambiguity may exist with

respect to the word (or phrase) that introduces each item. Consider the following

example:

Original version: This project will develop an intelligent solution for

large-scale industrial furnaces that can control large-scale interacting tem-

perature zones; deal with changes in load, fuel, and operating conditions;

and achieve optimal combustion. [192]

Clearly, this is a three-item list. The items are separated by semicolons because of the

embedded list in the second item. But what is the first item? There are two possibilities:

Possibility 1: The first item is the expression, develop an intelligent solution for large-scale industrial furnaces that can control large-scale interacting temperature zones. That is, the first word of all three items completes the compound verb that

begins with the word will (i.e., will develop, will deal, and will achieve) along with

the object of the compound verb.

Possibility 2: The first item is control large-scale interacting temperature zones.

That is, the first word of all three items completes the compound verb that begins

with the word can (i.e., can control, can deal, and can achieve) along with the

object of the compound verb.

The author can distinguish among these two possibilities by numbering the items in the

list. In the revised version below, the author has selected Possibility 2:

Revised version: This project will develop an intelligent solution for large-scale

industrial furnaces that can (1) control large-scale interacting temperature zones;

(2) deal with changes in load, fuel, and operating conditions; and (3) achieve

optimal combustion.

NUMBERED ITEMS IN A LIST 109

The second situation in which ambiguity can be avoided by numbering the items in a list

is where a subsequent item may be misinterpreted as a nonrestrictive qualifier of the

immediately preceding item. Consider the following example:

Original version: This fully-automated system will evaluate subjects referred

for SPECT imaging studies by extracting SPECT uptake values from 116

brain areas, generating 116 decay-corrected time activity curves, and inter-

facing the time activity curves to software modeling programs. [193]

Here, the ambiguity arises from the second participle phrase, generating 116 decay-corrected time activity curves. Again two possibilities exist:

Possibility 1: The participle phrase is a nonrestrictive qualifier that modifies the

first item of a two-item list or

Possibility 2: The participle phrase is the second item of a three-item list.

Again, the author can distinguish among the two possibilities by numbering the items:

Revised version: This fully-automated system will evaluate subjects referred for

SPECT imaging studies by (1) extracting SPECT uptake values from 116 brain

areas, (2) generating 116 decay-corrected time activity curves, and (3) interfacing

the time activity curves to software modeling programs.

Let’s look at one more example where one of the items of a list could be misinterpreted

as a nonrestrictive qualifier:

Original version: The development of nanostructured bulk thermoelectric

materials will combine innovations related to the production of nanopowders

of Bi2Te

3-Bi

2Se

3, a novel dispersion of matrix and additives, and the compac-

tion of these powders into high performance thermoelectric materials. [194]

In this case, the potential ambiguity arises from the phrase, a novel dispersion of matrix and additives. This phrase could be either (1) a further explanation of Bi

2Te

3–Bi

2Se

3

(i.e., a nonrestrictive explanatory phrase) or (2) the second item of a three-item list.

Numbering the items removes the ambiguity:

Revised version: The development of nanostructured bulk thermoelectric mate-

rials will combine innovations related to (1) the production of nanopowders of

Bi2Te

3-Bi

2Se

3, (2) a novel dispersion of matrix and additives, and (3) the compac-

tion of these powders into high performance thermoelectric materials.

Other Reasons to Use Numbers in ListsIn addition to avoiding ambiguity, three other situations may benefit from numbering

the items in a list. Each of these three situations will be presented in the context of an

example.

110 MULTIPLE-ITEM LISTS

In the first example, the items in the list occur in a particular sequence of steps; item (1)

precedes item (2), which precedes item (3), etc.:

1. Phase I will (1) prepare a concept design of the proposed elliptic beam

klystron; (2) design an elliptic-beam klystron interaction circuit using

small- signal theory; (3) design the elliptic klystron cavities; (4) perform 3D

simulations of the elliptic electron gun, beam compression, and matching;

and (5) develop a template for 3D simulation modeling of the small-signal

and large-signal elliptic-beam klystron interactions. [195]

In Example 2, a written number is used to introduce the list. The numbering of the two

items follows logically from the use of the word two in introducing the list:

2. The two most significant obstacles to the commercial production of bio-

oils from photosynthetic microalgae are (1) the low densities of cultures

associated with photosynthetic cultivation, and (2) the general difficulty of

extracting and purifying the bio-oils. [196]

In Example 3, numbering can help the reader distinguish among the items because some

of them are relatively long:

3. The approach will involve (1) a strain-compensated type II superlattice

structure, (2) a dark-current suppression technique for InAs/GaSb/AlGaSb

superlattice PIN diodes in the depletion region, and (3) an atomic-

hydrogen-enhanced growth and surface preparation technique. [197]